Field of the Invention
The invention relates to a microlens array and more particularly to a microlens array having a double-lens structure for use in a solid-state image sensor, and a method for fabricating the same.
Description of the Related Art
Recently, solid-state imaging sensors have been developed and are widely used in various image-capturing apparatuses, for example video cameras, digital cameras, minicam adapted personal computers, minicam adapted mobile phones, and so forth. Image sensors absorb incident radiation of a particular wavelength, such as visible light, UV light, IR light, or the like and generate an electrical signal corresponding to the absorbed radiation. There are a number of different types of semiconductor-based image sensors, for example charge-coupled device (CCD) image sensors or complementary metal-oxide semiconductor (CMOS) image sensors.
A solid-state imaging sensor typically consists of an array of pixels containing photo-sensors. Each photo-sensor in one respective pixel produces an electrical signal corresponding to an incident light irradiating on the photo-sensor in the image sensor. Therefore, the magnitude of the electrical signal produced by each photo-sensor is proportional to the amount of the incident light irradiating on the photo-sensor.
A microlens array is usually disposed over the solid-state imaging sensor to refract incident radiation to the photo-sensors. However, a large amount of incident light is not directed onto the photo-sensors. The sensitivity of solid-state imaging sensors cannot be improved due to lost light.